The invention relates to a light sensitive, aqueous-alkali developing, negatively functioning resist.
The greatest part of commercially available negatively functioning photoresists are in a nonaqueous form. Since in the case of these resists also in the case of resist processing, especially in the development of the illuminated resist areas, special organic solvents have to be used, the interest in their use is constantly reduced due to their increased environmental damage, and their limited performance parameter caused by the swelling of the resist during development (lack of dimensional stability in the transfer of the structural mask in the resist) [H. Bxc3x6ttcher; J. Bendig; M.-A. Fox; G. Hopf; H.-J. Timpe: Technical Applications of Photochemistry, Publ. Verlag fxc3xcr Grundstoffindustrie, Leipzig 1991, p. 178ff].
The Raycast-Series are used as aqueous alkali developing, nonswelling, negatively functioning photoresists [S. Nonogaki: Polym. J. 19 (1987), p. 99], and the Waycoat Resists [M. A. Toukhy; S. F. Mariotte: SPIE Advances in Resist Technology and Processing (1984), p. 86].
The main components of the Raycast-Series (with the resists RD 2000N, 1000N, and RG 3000N) polyvinylphenol (PVPh) is the polymeric binder, a resist-specific azide or bisazide as light sensitive components, and 2-methoxyacetate as solvent. The resist RD 2000N is used in the deep UV-range (DUV). The resists RU 1000N and RG 3000N are most sensitive in the UV range (308 nm, 313/320 nm, 365 nm) respectively in the UV/Vis range (365 nm, 406 nm, 436 nm). The light sensitive components in the resists RU 1000N and RG 3000N have only a limited solubility in the polymer solution, therefore the resists have a low solids content, suitably from 5% to 50% wt., most suitably from 5% to 35% wt. The maximum achievable film thicknesses of the resist applied to a substrate is 2 xcexcm.
PVPh has an excellent solubility, especially in the customary resist solvents but the high production costs represent a great drawback.
The Waycoat-resists are comprised of a novolac base as the polymeric binder. The employed novolac has only a small etching stability compared to basic solutions. The solvent is very toxic. The resist is sensitive in the DUV range.
The object of the invention includes the preparation of a light sensitive, aqueous alkali developing, negatively functioning resist comprised of a polymeric binder having good solubility properties, and a high etching stability, and a light sensitive component, which has a high sensitivity and high photoreactivity over a wide spectral range, and has good solubility characteristics in the polymeric solution, and its light sensitive components can be prepared by an economical process.
The present invention is a light sensitive, acqueous alkali developing, negatively acting resist, comprising a phenolic resin as binder, a light sensitive component of a diazostilbene-disulfonic acid ester of Formula (I) 
wherein R1 is a residue of Formula (II) 
wherein R2 and X are independently of each other hydrogen, or a branched or straight chain alkyl residue, and n is a cardinal number from 1 to 10, a solvent or mixture of solvents, and film forminmg and/or a film stabilizing additive.
The invention also relates to a process for producing the diazostilbene-disulfonic acid ester light sensitive component, which comprises sulfochlorinating a diazostilbene disulfonic acid disodium salt with thionyl chloride, suitably an excess of thionyl chloride, so that a stoichiometric amount of the dimethylformamide based on the amount of the disodium salt is employed, and reacting in the presence of acid binding additives the resulting diazostilbene disulfochloride with an alcohol of Formula III 
wherein R2 is hydrogen, a branched and unbranched alkyl residue, X is hydrogen, a branched or unbranched alkyl residue, and n is a cardinal number from 1 to 10.
The invention also relates to a process for the lithographic production of negative structures for the xcexcm -and -nm range, characterized in that a photoresist is employed, which comprises a phenolic resin, a light-sensitive component of Formula (I), a solvent or solvent mixture, and film forming or film stabilizing additives, applying the resist as a film to the substrate, the film being suitably formed on the substrate by spincoating, roller coating, moistening coating, spray coating, or dip coating to form a resist film suitably of from 0.3 xcexcm to 10 xcexcm thickness, drying the resist film suitably from 1 minute to 60 minutes ay from 60xc2x0 C. to 120xc2x0 C., exposing the resist film to an image in the wavelength range of 200 nm to 400 nm suitably with a high pressure lamp or a laser, developing the film with an aqueous alkaline developer, suitably an alkali metal ion-containing developer at a concentration of from 0.2% wt. to 1.5% wt., or in a metal ion-free developer of a concentration of from 1% wt. to 5% wt. suitably for a period of from 10 to 15 minutes, and drying the resulting structure.
As the polymeric binder, a novolac (phenol-formaldehyde/cresol-formaldehyde condensate) can be employed as an alternative to the PVPh. This novolac is substantially less costly to use; it is soluble in acetone and in aqueous alkaline solutions.
Nontoxic solvents are advantageously used in the resist, suitably in the form of esters, ketones, alcohols or mixtures thereof.
In producing the light sensitive component, suitably p[yridine, NaOH, or a caustic alkali is added to the reaction mixture.
The diazidostilbene-disulfonic acid ester light sensitive component has excellent solubility in the aforementioned solvents and in the polymer solution, which enables a high solids content in the resist. Due to the high photoreactivity and the broad spectral sensitivity of these compounds in the range of 200 to 400 nm (DUV -and UV range) the illumination of the resist layers is possible by using the currently used quartz optics and with the customary glass optics.
The solids content of the resist and thus the content of light sensitive components in the solids is variable within wide ranges so that as desired film thicknesses can be obtained from 0.3xcexcm to 10 xcexcm.
The resist can suitably further contain surfactants, smoothers, or adhesives as filmforming and/or film stabilizing additives.
The cost advantageous synthesis of a diazostilbene-disulfonic acid ester light sensitive component can be carried out in a simple two-step process, with high yield.
The use of environmentally friendly and nontoxic, aqueous developers is of particular advantage.
The resist of the invention is suitable for use in standard (AZ-compatible) lithographic processes, to create microstructures to a resolution of  less than 0.5 xcexcm, which have a high dimensional stability (1:1 transfer of the structure of the mask in the resist), high edge sharpness, and very good etching stability.